atxmega128a3-mu ATMEL Corporation, atxmega128a3-mu Datasheet - Page 19

• Manufacturer Part Number: atxmega128a3-mu
• Description: 8/16-bit Xmega Microcontroller
• Manufacturer: ATMEL Corporation

12. System Control and Reset
12.1
12.2
12.2.1
12.2.2
12.2.3
12.2.4
12.2.5
12.2.6
12.2.7
8068A–AVR–02/08
Resetting the AVR
Reset Sources
Power-on Reset
External Reset
Watchdog Reset
Brown-out Reset
JTAG AVR Reset
PDI reset
Software reset
During reset, all I/O Registers are set to their initial values. Application execution starts from the
Reset Vector. The instruction placed at the Reset Vector should be a JMP - Absolute Jump -
instruction to the reset handling routine. If the application never enables an interrupt source, the
Interrupt Vectors are not used. The regular application code can then be placed at these loca-
tions. This is also the case if the Reset Vector is in the Application section while the Interrupt
Vectors are in the Boot section or vice versa.
The I/O ports of the AVR are immediately tri-stated when a reset source goes active.
The reset functionality is asynchronous, hence no running clock is required to reset the device.
The reset source can be determined by the application by readig a reset status register. The
XMEGA A3 has the following sources of reset:
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The MCU is reset when the supply voltage VCC is below the Power-on Reset threshold voltage.
The MCU is reset when a low level is present on the RESET pin.
The MCU is reset when the Watchdog Timer period expires and the Watchdog Reset is enabled.
The MCU is reset when the supply voltage VCC is below the Brown-out Reset threshold voltage
and the Brown-out Detector is enabled.
The MCU is reset as long as there is a logic one in the Reset Register, one of the scan chains of
the JTAG system. Refer to IEEE 1149.1 (JTAG) Boundary-scan for details.
The MCU may be reset through the Program and Debug Interface (PDI).
The MCU may be reset by the CPU writing to a special I/O register.
Power-on Reset
External Reset
Watchdog Reset
Brown-out Reset
JTAG AVR Reset
PDI reset
Software reset
ATxmega A3
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